Click for next page ( 30


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 29
29 APPENDIX Recommended Test Methods The proposed test methods, prepared as part of NCHRP Project 14-17, Manual for Emulsion-Based Chip Seals for Pavement Preservation, are the recommendations of the NCHRP Project 14-17 staff at Colorado State University. These test methods have not been approved by NCHRP or any AASHTO committee nor have they been accepted as AASHTO specifications. CONTENTS Recommended Standard Method of Test for Embedment Depth of Chip-Seal Aggregates in the Lab and the Field, 30 Recommended Standard Method of Test for Laboratory Chip Loss from Emulsified Asphalt Chip Seal Samples, 39 Recommended Standard Method of Test for Measuring Moisture Loss from Chip Seals, 53 Recommended Standard Method of Test for Recovery of Asphalt from Emulsion by Stirred-Can Method, 59 Recommended Standard Method of Test for Determining the Strain Sensitivity of Asphalt Emulsion Residue Using Strain Sweeps Performed on a Dynamic Shear Rheometer (DSR), 63

OCR for page 29
30 Recommended Standard Method of Test for Embedment Depth of Chip-Seal Aggregates in the Lab and the Field AASHTO Designation: Txxx-xx 1. SCOPE 1.1 This test method provides the average aggregate embedment depth, in asphalt, of field chip seals and laboratory specimens. 1.2 The values stated in SI units are to be regarded as the standard unless otherwise indicated. 1.3 A precision and bias statement for this standard has not been developed at this time. Therefore, this standard should not be used for acceptance or rejection of a material for purchasing purposes. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1 ASTM Standard: D 8, Terminology Relating to Materials for Roads and Pavements 3. SUMMARY OF TEST METHOD 3.1 Where the void ratio of an area of chip seal may be estimated with acceptable accuracy, and where voids (Note 1) between all chip-seal particles are filled with a given mass of glass beads of known packing density, the average height of beads within the chip seal layer may be determined. This average height of beads between the surface level of the asphalt and the average height level of the chip- seal particles would reflect the chip seal's texture height. Given the average particle height of the chip-seal aggregate, one may perform a calculation, using the evaluated texture height, to yield the chip-seal embedment depth.

OCR for page 29
31 Note 1--For the purposes of this test method, it is assumed that the actual chip- seal voids are those that exist above the asphalt surface and below the profile of an imaginary, three-dimensionally undulating, flexible membrane that is draped over aggregate particles and forced to come into contact with the peak of each particle (see Figure 1 and Figure 2). Imaginary undulating Volume of surface: upper bound of chip seal voids chip seal voids Height of average particle T H Chip Seal E Bedding Plane Asphalt Aggregate Figure 1. Undulating profile over particle peaks and voids. Imaginary undulating Voids Profile of voids Volume of surface: upper bound of filled by remains unchanged chip seal voids chip seal voids asphalt at all embedments Height of average T particle H E Chip Seal Bedding Plane Asphalt Aggregate Figure 2. Profile remains unchanged at all embedments.

OCR for page 29
32 Two procedures are provided, each of which may be used to evaluate a field chip seal or a specimen chip seal for embedment depth. In the first, the "spreading procedure," a known, fixed volume of glass beads is spread into a circular area over the surface of a chip seal to fill the voids between the particles, which are illustrated in Figure 1. The glass beads bridge between the peaks of the chip-seal particles in all directions and form an undulating profile. Effectively the average height of glass beads covering the specimen is the same as the height of the chip seal's average particle (Note 2). The circular area, achieved with the fixed volume of glass beads, is used to evaluate embedment depth. Note 2--For simplification, it is assumed that an "equivalent" chip seal, constructed with one-sized, identical particles, each with height equal to the average particle height, may be substituted for the actual chip seal that contains voids as defined in Note 1. It is further assumed that the constituents of such an equivalent chip seal, of the same area as the actual chip seal, would precisely reflect the height of asphalt and the volumes of asphalt, aggregate particles, and voids that exist in the actual chip seal. In this regard, the texture height is the height between the level of the asphalt surface and the level of the top of particles in the equivalent chip seal (Figure 3). Volume of chip seal voids Height of average particle T H Chip E Seal Bedding Plane Asphalt Aggregate Figure 3. Equivalent chip seal. In the second procedure, the "submerging procedure," a known, variable volume of glass beads is used to completely cover all chip-seal particles within a fixed area to a fixed level above the height level of the chip seal's average particle (Figure 4). In order to determine the volume of beads within the chip-seal voids, a calculation is first performed using the concept of the flat-topped equivalent chip seal (Note 2) to determine the excess volume of beads that occupies the space above the chip seal (Figure 5). The void volume is obtained by subtracting the excess volume of beads from the total volume of glass beads on the chip-seal area. This allows for evalua- tion of the embedment depth.

OCR for page 29
33 Imaginary undulating "C" is the volume of all beads Glass beads, surface: upper bound of deposited directly on the chip Glass beads, "C B," chip seal voids seal of fixed area "A" "B," in voids above voids Top of mold Height of average particle T M H Chip Seal E Bedding S Plane Mold of area Base (optional), of Asphalt Aggregate "W" area "R," under laboratory chip seal Figure 4. Submerging procedure. "C" is the volume of all beads Excess beads, deposited directly on the chip Glass beads, "C B," seal of fixed area "A" "B," in voids above chip seal Top of mold Height of average particle T M H Chip E Seal Bedding S Plane Mold of area Base (optional), of Asphalt Aggregate "W" area "R," under laboratory chip seal Figure 5. Equivalent model for the submerged chip seal. Note 3--The submerging procedure, which may be used for any degree of embedment, has been devised primarily to account for the situation, at very high embedment depths, where the asphalt surface intersects the imaginary membrane defined in Note 1. In this situation, where some particle peaks are covered, it may become difficult to spread the beads to follow the required profile illustrated in Figure 2.

OCR for page 29
34 4. SIGNIFICANCE AND USE 4.1 This test method is intended to be used in the evaluation of embedment depth in field and specimen chip seals. 4.2 In predicting future performance of a chip seal, embedment depth evaluation is critical. This is because performance, in certain aspects such as reduced aggregate loss, is likely to increase as embedment depth increases. Performance in terms of high skid resistance and reduced construction cost, on the other hand, is likely to decrease with increased embedment beyond a certain level. 4.3 Additionally, embedment depth evaluation is important simply because it is often the only practical means by which an apparently sound field chip seal may be evaluated. 4.4 Ultimately, the results of embedment depth evaluations enable better quantification of the relative risk associated with apparently sound roads. 5. APPARATUS 5.1 Balance The balance must be capable of weighing approximately 10,000 g of glass beads per square meter of chip seal to within +0.1 g. 5.2 Glass Cylinder/Container A smooth-bottomed glass cylinder is to be used for the spreading procedure. A drinking glass (a shot glass) used for this purpose also doubles as a container for weighing glass beads and pouring them onto the chip- seal surface. 5.3 Measuring Tape This is used to measure the diameter of glass bead circles achieved using the spreading procedure. The tape is to be graduated in millimeters. 5.4 Laboratory Mold Used in the submerging procedure in the laboratory, the mold is to have a constant height (M) and a constant cross sectional area (W) large enough to accommodate the specimen chip seal. Additionally, when filled to its rim, the mold must provide for complete submergence of the specimen chip seal. Note 4--The top elevation of the mold needs only to be some 3 mm higher than the tallest chip seal particle in order to allow smooth screeding of the surface. 5.5 Working Platform For precision, the specimen chip seal and laboratory mold should always be prepared and configured on a flat and level platform.

OCR for page 29
35 5.6 Offset Spacers To perform the submergence procedure in the field, offset spacers of known height are used to establish an offset distance from the bedding plane of the chip seal. The tops of the spacers are equidistant from the bedding plane and higher than the average particle height in order to achieve submergence of chip-seal particles. Note 5--The submerging procedure is not a suitable candidate on steeply sloping roadways or where the level of the bedding plane is unknown. The procedure is suitable on areas where the bedding plane level has been recorded and where the plane is flat and approximately level in the area to be tested. 5.7 Field Mold When carrying out the submerging procedure in the field, a field mold is to be used to form the glass beads over a fixed area of chip seal. The field mold is to be built up using a perimeter gasket wall and a flat metal surface with a cutout. The vertical-faced gasket wall, which may consist of moldable putty or silicone, must be shaped such that it dams the spaces between chip-seal particles and finishes flush with the cut-out area of the metal surface. Placement of the metal surface is to be accommodated by the use of offset spacers such that it is flat, at a known height above the average chip-seal particle, and allows full submergence of the chip seal. 6. PREPARATION OF MATERIALS 6.1 Specimen Chip Seal For the purposes of this test method, a specimen chip seal is constructed on a flat and level base, or sheet, of known thickness (S) and area (R). Additionally, for the submerging procedure, it must be possible to place the specimen into a mold or to form a mold around the chip seal. 6.2 Area of Chip Seal Precisely measure the chip seal area (A), which is being evaluated for embedment. 6.3 Glass Beads These are fine particles of glass that are able to fit between chip- seal particles and, en masse, follow the contours of the particles' surface. 6.4 Packing Density of Glass Beads Fill the tared mold, of known volume (K), with glass beads and weigh the filled container. Establish the packed glass beads' mass per unit volume (P) for use in the following procedures. 7. SPREADING PROCEDURE IN THE LAB AND IN THE FIELD 7.1 Using the tared glass cylinder/container, weigh out a pre-calculated mass of glass beads that will provide a chosen volume (B) at a packed density (P) (defined in section 6). Record the mass to the nearest 0.1 g.

OCR for page 29
36 7.2 Pour the glass beads onto the center of the specimen to form a pile. Position the glass cylinder on the pile of glass beads and move it in a circle to spread the beads into a circular area. 7.3 Use the fingers to continue spreading the beads outward in a circle while allowing the beads to accumulate between particle peaks, completely and exactly filling the void volume (Note 1). This is achieved when only the highest point of each aggregate particle (not otherwise submerged by asphalt) is exposed. 7.4 Place a marker at the approximate center of the circular area of beads. Rotating about the marker, take four diameter measurements, with the measuring tape, in line with the marker and rotationally offset 45 degrees from each other. Calculate the average circle diameter (D). 8. SUBMERGING PROCEDURE IN THE LAB AND IN THE FIELD 8.1 Weigh and record, to the nearest 0.1 g, the mass of a volume (Y) of glass beads, which will be more than enough to cover the chip seal and fill the mold. 8.2 For the lab procedure, place the specimen chip seal into the mold or form the mold around the specimen, ensuring that the mold and the specimen are flat and level and that complete submergence of the chip seal will be achieved. 8.3 For the field procedure, install the offset spacers such that they are elevated a known height above the bedding plane of the chip seal as a guide for the installation height of the field mold. 8.4 Sweep the field chip seal clean and install the mold over the area to be evaluated such that the mold's top surface is flat and at a known offset distance above the bedding plane of the chip seal. 8.5 Pour glass beads into the mold and screed the surface of the beads flush with the top of the mold. The chip-seal aggregate particles should be completely covered by glass beads. 8.6 Carefully recover the glass beads that were screeded off the mold. Weigh the unused portion of beads and calculate the total mass of beads deposited into the mold. In turn, use this result along with the packing density (P) to calculate the total volume (G) of beads deposited into the mold. 8.7 For laboratory molds that are larger in area than the specimen chip seal, also calculate the volume of beads (C) (section 9), which is deposited directly on the chip seal surface area under evaluation.

OCR for page 29
37 9. CALCULATIONS 9.1 The chip seal's texture height (T) is the average height dimension of the un-embedded portion of particles. The average height level of this un-embedded portion is the same as the average height level of the chip-seal particles. Therefore, the texture height is equivalent to the dimension difference between the depth of asphalt (E) and the average particle height (H). Where a volume of beads (B) is shaped such that it fills the chip seal voids, the texture height can be calculated from the following: volume of beads and aggregate above the asphalt surface T= plan area of beads and aggregate That is: T = {B + [T (1 V) A]}/A; T = B/(A * V) (1) And the embedment is obtained using the following: E=HT (2) Where T = texture height (mm), B = volume of glass beads (mm3) on the chip seal surface, filling only voids between particles, A = plan area of chip seal covered by beads (mm2), V = the void ratio, E = the particle embedment depth in asphalt (mm), and H = the average particle height (mm). Where the submerging procedure has been used, whether in the lab or in the field, obtain B by subtracting the volume of beads that would lay above the top level of an equivalent chip seal (Note 2) from the total volume (C) of beads filling the voids and submerging the chip seal (Figures 4 and 5). B = C [(M S H ) * A] (3) Where B = volume of glass beads (mm3) on the chip-seal surface, filling only voids between particles; C = total volume of beads (mm3) deposited directly on the chip-seal surface area; S = thickness of base, or sheet, on which specimen chip seal has been constructed (mm) (Note: S = 0 for field chip seals); M = height of top of mold (mm) above bottom level of chip-seal base; H = the average particle height (mm); and A = plan area of chip seal covered by beads (mm2).

OCR for page 29
38 For laboratory specimens where the plan area of the mold is larger than that of the chip seal under evaluation, obtain C using the following: C = G [(WM ) (RS ) (A{M S})] (4) Where C = total volume of beads (mm3) deposited directly on the chip-seal surface area; G = total volume of beads (mm3) deposited into the mold; W = area of mold (mm2); M = height of top of mold (mm) above bottom level of chip seal base; S = thickness (mm) of base, or sheet, on which specimen chip seal has been constructed; R = area of base (mm2); and A = plan area of chip seal covered by beads (mm2).

OCR for page 29
39 Recommended Standard Method of Test for Laborator y Chip Loss from Emulsified Asphalt Chip Seal Samples AASHTO Designation: Txxxx-xx 1. SCOPE 1.1 This test method measures the quantity of aggregate lost, at variable moisture levels of systems of asphalt emulsion and aggregate chips, by simulating the brooming of a chip seal in the laboratory. 1.2 The values stated in SI units are to be regarded as the standard unless otherwise indicated. 1.3 A precision and bias statement for this standard has not been developed at this time. Therefore, this standard should not be used for acceptance or rejection of a material for purchasing purposes. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1 AASHTO Standards: T 19, Standard Test Method for Bulk Density ("Unit Weight") and Voids in Aggregate T 85, Test Method for Density, Relative Density (Specific Gravity), and Absorption of Coarse Aggregate T 27, Sieve Analysis of Fine and Coarse Aggregates T 2, Practice for Sampling Aggregates T 40, Practice for Sampling Bituminous Materials M 140, Specification for Emulsified Asphalt M 208, Specification for Cationic Emulsified Asphalt 2.2 ASTM Standards: D 226, Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing D 7000, Standard Test Method for Sweep Test of Bituminous Emulsion Surface Treatment Samples

OCR for page 29
55 6. MATERIAL PREPARATION 6.1 Specimen Board Each chip-seal specimen is manufactured on an 18-in. square and 3/16-in. thick plywood board (Figure 1) with an unconditioned surface. A continuous, light gauge, z-shaped metal strip is fixed to the perimeter of the board. The vertical legs of the z-shaped metal strip are oriented such that the board is suspended in. above the pavement by one leg (the inner) of the z-shaped metal edging (for easy removal from the roadway) while the other leg forms a vertical lip protruding above the surface of the board (to prevent the loss of any specimen material as the board is moved). 18 inch square plywood board z- shaped metal edging on board- perimeter Figure 1. Configured specimen board. 6.2 Aggregate and Asphalt Emulsion The chip-seal specimens are laid down by the distributor and chipper in the course of placing the actual field chip seal. In this regard, the properties of the specimen aggregate and asphalt emulsion are those of the field chip seal. 6.3 Aggregate Sample the aggregate from the stockpile that is to be used in the manufacture of the chip seal and store in an airtight container. Where moisture content tracking is to be performed without the need for immediate results on site, laboratory determination of aggregate moisture content (W ) may be performed. Alternatively, estimate moisture content (W ) according to Note 2 where immediate moisture content results are required and where available time, sufficient resources, and the need for higher on-site accuracy warrant extra care. Note 2--An acceptable on-site approximation of the aggregate moisture content may be obtained by drying a representative sample of chip-seal aggregate over a few hours of the workday. Place approximately 3 kg of aggregate (in its sample state) on the tared drying pan and record the wet aggregate mass. Place the drying pan and its contents in a warm (and, preferably, windy) location. When the aggregate becomes dry to the touch, record the mass loss of the aggregate. The aggregate moisture content (W ) is the mass loss expressed as a percentage of the dried aggregate mass. 6.4 Asphalt Emulsion Usually, a good approximation of the project asphalt emulsion's residual content (R) may be obtained from key site personnel. Where dependable figures are not available, the cure level of the chip seal must be based on conservative and conventional figures (approximately 70% residual content) until a simple lab experiment can be performed such as that outlined in Note 3.

OCR for page 29
56 Note 3--To evaluate the residual content of the asphalt emulsion that was used on site, dry approximately 50 g of the material, weighed to the nearest 0.1 g, in a 100C oven, in the laboratory, to obtain the residual asphalt. The asphalt emulsion should be placed in a thin layer in an approximately 11-in.-diameter aluminum foil pan. Monitor the mass of the material until it no longer continues to lose mass over two consecutive readings taken 8 h apart. Record the mass loss and the final residual asphalt mass to the nearest 0.1 g. Estimate the moisture content of the asphalt emulsion to be the mass loss expressed as a percentage of the initial asphalt emulsion mass. The asphalt emulsion's residual content (R) is the final residual asphalt mass expressed as a percentage of the initial asphalt emulsion mass. 7. SPECIMEN MANUFACTURE AND WEIGHING 7.1 Set up the weighing platform (with optional wind shield) in an off-road location within short walking distance of the location where the specimen is intended to be manufactured. Level the platform and position the scale on the platform (with optional pedestal). 7.2 Record the tare mass (B) of an unused specimen board. 7.3 Place the weighed specimen board at a chosen location on the roadway (Note 4) that is to be chip sealed. Ensure that the board is not positioned in the wheel paths of the distributor, chipper, or other trucks. Note 4--Locations at which specimen chip seals are to be made should be chosen based on the availability of similar off-road locations, in terms of temperature and exposure, to where the specimen may be cured. Additionally, at selected manufacture locations, manufacture should be fast and allow for removal and weighing of the specimens within 5 min of the asphalt emulsion being sprayed onto the board. When monitoring the field chip seal, observations should be made at a location immediately adjacent to where the specimen is manufactured. 7.4 Immediately after chips have been dropped onto the specimen board, move the specimen from the roadway and obtain its initial total mass reading (S). 7.5 Obtain the asphalt emulsion spray rate (E) from appropriate site personnel. 7.6 Throughout the workday, maintain a log of the temperatures and other environmental conditions affecting the cure rates of the specimen and the field chip seals. Relocate the specimen as necessary to ensure similar curing conditions relative to those of the field chip seal.

OCR for page 29
57 7.7 Record the total mass (C ) of the specimen as it cures throughout the day to various cure levels. Note 5--Record the specimen mass as often as practical but at least once per hour until a desired cure level has been achieved. 7.8 Where curing conditions throughout the workday are similar for the specimen and the field chip seal, it may be assumed that the chip-seal moisture content at a certain time after construction is approximated by that of the specimen. 8. CALCULATIONS 8.1 The mass of asphalt emulsion in the specimen is obtained from the following: O = 3785 (UEAG) (1) 8.2 The mass of dry specimen aggregate is obtained from the following: D = (S B O)/(1 + W ) (2) 8.3 The initial mass of all specimen moisture is obtained from the following: I = S B D (OR) (3) 8.4 The mass of all specimen moisture at cure level (L) is obtained from: F = C B D (OR) (4) 8.5 The percent moisture content of asphalt emulsion at cure level (L) is obtained from: M = [100F ]/[(OR) + F ] (5) 8.6 The cure level of the specimen asphalt emulsion is obtained from: L = 1 {F/[O (1 R)]} (6)

OCR for page 29
58 Where O = mass of asphalt emulsion on the specimen board (g), U = unit weight of water (g/ml), E = reported emulsion spray rate (gal/sy), A = specimen board area (sy), G = specific gravity of the asphalt emulsion, D = mass of dry specimen aggregate (g), S = initial specimen mass (including board) (g), B = mass of the specimen board (g), W = initial percentage moisture content of specimen aggregate (as percentage of dry aggregate mass), I = initial mass of all specimen moisture (emulsion and aggregate moisture) (g), F = moisture mass in specimen at cure level (L) (g), C = specimen mass (including board) at cure level (L) (g), L = the cure level at which specimen moisture content is being evaluated, M = percentage specimen moisture content at cure level (L) (as percentage mass of current asphalt emulsion), and R = percentage residual asphalt content of emulsion (as percentage mass of initial asphalt emulsion).

OCR for page 29
59 Recommended Standard Method of Test for Recover y of Asphalt from Emulsion by Stirred-Can Method AASHTO Designation: Txxxx-xx 1. SCOPE 1.1 This method covers the recovery of asphalt from a water-based emulsion by the stirred- can evaporation method. The recovered asphalt reproduces the asphalt with the same properties as those used as the asphalt base in the emulsion and in quantities sufficient for further testing. 2. SUMMARY OF METHOD 2.1 The water in the asphalt emulsion is evaporated under a nitrogen atmosphere at an elevated temperature. Initially, the set point for the emulsion temperature is above the boiling point of water, but the temperature of the emulsion would stay at the boiling point of water while the evaporating process occurs. After most of the water has been evaporated, the temperature of the emulsion will increase to the initial set point and the remaining water will be completely removed. The recovered asphalt (evaporation residue) can then be subjected to further testing as required. 3. APPARATUS 3.1 Laboratory Mixer The standard laboratory mixer with mixing blade and shaft that is capable of reaching a mixing speed of 1,000 to 2,000 rpm. 3.2 Tin Can The can should have a volume capacity of 1 gal with a 6-in. diameter to allow adequate access of mixing head, thermocouple, and nitrogen outlet. 3.3 Heating Unit The heating unit consists of the heating tape and the Variac, which is used to control output power. The length of heating tape should be adequate to wrap around the tin can until it fully covers the bottom half of the can. 3.4 Nitrogen Purge and Nitrogen Blanket System As shown in Figure 1, these should consist of a nitrogen piping system, nitrogen purge blanket, nitrogen sparge ring, and rotameters that are capable of measuring the gas flow up to 8.5 to 10 L/min. 3.5 Temperature Controlling Unit The temperature control and thermocouple must be able to operate at the maximum temperature of 325 F. 3.6 Heat Insulator The insulator pad should be large enough to cover the tin can that is wrapped with heating tape to prevent the heat from the tape escaping to the atmosphere. 4. REAGENTS AND MATERIALS 4.1 Liquid Nitrogen A pressurized tank, with regulator or pressure-reducing valve.

OCR for page 29
60 5. SAMPLE 5.1 The sample must be a water-based asphalt emulsion. If a solvent-based emulsion is used, the set point temperature may need to be changed to ensure completion of solvent removal. Also, the properties of the recovered binder may not agree with the base asphalt if there is solvent residue left in the recovered binder. 5.2 Generally, asphalt binder will progressively harden when exposed to air, especially if the asphalt is placed in a high-temperature environment. Therefore, during the recovery process, the emulsion must be under a nitrogen atmosphere when the solvent is evaporated at a high temperature. 2 3 4 5 1 6 7 Figure 1. Schematic view of stirred-can setup: (1) Gallon can, (2) Thermocouple, (3) Impellor and shaft, (4) N2 blanket tube, (5) N2 sparger, (6) Heat tape, and (7) Thermal insulation. 6. PROCEDURE 6.1 The experimental setup for the stirred-can procedure is shown in Figure 1. 6.2 Weigh 1,250 0.5 g of asphalt emulsion and add to the gallon can, then wrap the heating tape around the can until the tape covers the bottom half. Cover the side of the can with the heat insulation pad and place the container underneath the laboratory mixer. 6.3 Place the sparge ring into the can, but to prevent overflow due to foaming, do not turn the nitrogen sparge on at the beginning.

OCR for page 29
61 6.4 Lower the mixer head into the emulsion can and turn the mixer on. Then place the lid on top of the container and increase the mixing rate to 1,000 to 2,000 rpm, depending on how thick the emulsion is. After that, insert the thermocouple into the can. To ensure accurate temperature controlling, the thermocouple should not touch the side of the can or mixer head. 6.5 Turn on and adjust nitrogen flow to 8.5 to 10 L/min for the nitrogen blanket tube, then place the nitrogen blanket outlet on the emulsion surface to create a nitrogen blanket. 6.6 Connect the heating tape with the Variac and turn the Variac on to begin the heating process, then set the temperature controller to 163C (325F). The Variac providing power for the heating tape is set to 140 V, with corresponding power of approximately 430 W. After the heat is supplied to the system, the foaming process will start to occur. 6.7 Change the voltage on the Variac to about 100 V (corresponding power is 260 W) when the emulsion temperature reaches 100C (212F). The time from the beginning of the experiment to the time to change the voltage is approximately 20 to 30 min. Also, if foaming stops, start the nitrogen flow into the sparge ring (8.5 to 10 L/min). The emulsion temperature should stay at the boiling point of water until the majority of the water is evaporated; the emulsion temperature will then start to increase. 6.8 Let the emulsion temperature reach 325F and wait for 10 min at this temperature (total recovery time is approximately 180 min). After 10 min, turn off the Variac, remove the heat insulation, and loosen the heat tape, but maintain the nitrogen flows and stirring while the sample is cooling. 6.9 Figure 2 shows a typical temperature versus time evolution curve. Four regions are evident. The first one is from the beginning to about 18 min. In this region, the temperature increases rapidly and nearly linearly from room temperature (around 72F, or 22C) to 212F (100C). The water evaporation rate is low in this region, and power input primarily increases the temperature. The second region is between 18 min to 110 min where the temperature increases slowly from 212F (100C) to 250F (121C) in about 90 min. Here the power input mainly provides water evaporation. The third region is between 110 min to 135 min, where the temperature increases linearly from 250F (121C) to 325F (163C) in about 25 min, a slower rate than in the first region. In this region, much of the water has evaporated and the power input primarily increases the temperature. In the fourth region, from 135 min to the end of the experiment at 170 min, the temperature is controlled at 325F (163C). (In Figure 2, the temperature evolution after 150 min is not shown because it changes little.) 6.10 As the sample starts to cool (<200F), take out the nitrogen sparge ring but keep nitrogen flowing through the tube to prevent clogging. Then stop the mixer and move the mixer head upward. 6.11 Store the sample in a cool room (25C). The recovered sample can be used for further testing.

OCR for page 29
62 350 Temperature (F) 300 250 200 150 100 50 0 50 100 150 Time (min) Figure 2. Temperature evolution of the recovery system.

OCR for page 29
63 Recommended Standard Method of Test for Determining the Strain Sensitivity of Asphalt Emulsion Residue Using Strain Sweeps Performed on a Dynamic Shear Rheometer (DSR) AASHTO Designation: Txxxx-xx 1. SCOPE 1.1 This test method covers the determination of strain sensitivity of asphalt residue from a water-based emulsion from changes in the dynamic shear modulus obtained from strain sweeps performed using the dynamic shear rheometer (DSR). This test method is supplementary to AASHTO T 315 and incorporates all of that standard. For this test method, the asphalt binder is the residue obtained by removing the water from a water- based asphalt emulsion. 1.2 This standard is appropriate for unaged material or material aged in accordance with R28. 2. REFERENCED DOCUMENTS 2.1 AASHTO Standards: T 315, Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer M 320, Performance-Graded Asphalt Binder R 28, Accelerated Aging of Asphalt Binder Using a Pressure Aging Vessel (PAV) R 29, Grading or Verifying the Performance Grade (PG) of an Asphalt Binder T40, Sampling of Bituminous Materials 2.2 ASTM Standard: E1, Specification for ASTM Thermometers 3. SUMMARY OF TEST METHOD 3.1 This standard contains the procedure used to measure the complex shear modulus (G*) of asphalt residues from water-based emulsions using a DSR and parallel plate test geometry. 3.2 The standard is suitable for unaged material or material aged in accordance with R28. 3.3 The standard is suitable for use when the emulsion residue is not too stiff to be torqued by the DSR.

OCR for page 29
64 4. SIGNIFICANCE AND USE 4.1 The temperature for this test is related to the test temperature experienced by the pavement maintenance treatment in the geographical area for which the asphalt emulsion is to be applied. Typically the maintenance treatment is applied at moderate ambient temperature, and a default temperature of 25C can be used for the strain sweep evaluation. 4.2 A plot of dynamic shear modulus G* versus time will be generated and compared as an indication of strain sensitivity of the residue. 4.3 The complex shear modulus is an indication of the stiffness and the resistance of the asphalt residue to deformation under load and also is an indication of the ability of the residue to hold aggregate. 5. APPARATUS 5.1 Dynamic Shear Rheometer Test System Consisting of parallel metal plates, an environmental control system, a loading device, and a control and data acquisition system. 5.2 Test Plates The 8-mm plates are used for this test with a 2-mm gap. The preliminary gap before trimming must be set to achieve an acceptable bulge in the material after trimming. 6. REAGENTS AND MATERIALS 6.1 Varsol or another suitable agent for cleaning the plates. 6.2 Acetone for removal of all remaining residue from the plates. 7. SAMPLE 7.1 The sample is the residue after the water is removed from the water-based asphalt emulsion. The properties of recovered binder may not agree with the base asphalt since other substances have been added to the base binder in the emulsification process. 8. PROCEDURE 8.1 Procedure is as described in AASHTO T 315 using the 8-mm plates with a 2-mm gap. 8.2 Prepare the emulsion residue specimen according to AASHTO T 315. 8.3 Place the sample in the DSR and trim it according to AASHTO T 315.

OCR for page 29
65 8.4 Bring the sample and the environmental system to thermal equilibrium according to the manufacturer's directions and AASHTO T 315. 8.5 Perform the strain sweep. 8.6 Use the following parameters for the strain sweeps: Intermediate test temperature, with 25C being the default temperature. For strain sweeps, the DSR is set in oscillation mode for amplitude sweeps. DSR is set for auto-stress so that stress will be automatically adjusted to achieve desired strain. Frequency is set to 10 radians per second. Initial stress is set to the lowest stress that the DSR is capable of applying. Strain is set to increment between 1% and 50%, or between 1% and the highest strain that the DSR can achieve with the material being tested. A preliminary test may be needed, especially with stiff residues, to estimate the highest strain percent that can be set for the test. Steady shear rate is set to zero and is not used in this test. Number of periods is set to 1. Number of points is set to 256. Number of samples can be between 20 and 30. Determine the number of samples to test at enough points to define the strain sweep curve when plotting G* versus time. Strain control sensitivity is set to medium or better. Shear strain sequence is set for "up" so that strains are incremented from low to high. Time increments are set to linear so that the time increments between measurements are approximately linearly chosen (not logarithmically). Delay time is set to 1 s. Check that integration time is between 1 and 2 s, and total test time for the strain sweeps is less than 2 min. 8.7 Visually inspect the sample after the test when removing the sample from the plates. Note whether the sample is wholly or partially adhered to the plates, and note whether the sample has a ductile or a brittle break when the plates are pulled apart. 8.8 Generate a plot of dynamic shear modulus versus time. A flat curve indicates a strain- resilient material. A steep curve indicates a strain-sensitive material.